Layerwise heating, linewise heating, plasma heating and multiple feed materials in additive manufacturing

ABSTRACT

An additive manufacturing system that includes a platen, a feed material delivery system configured to deliver feed material to a location on the platen specified by a computer aided design program and a heat source configured to raise a temperature of the feed material simultaneously across all of the layer or across a region that extends across a width of the platen and scans the region across a length of the platen. The heat source can be an array of heat lamps, or a plasma source.

CLAIM OF PRIORITY

This application claims priority under 35 USC §119(e) to U.S. PatentApplication Ser. No. 62/022,428, filed on Jul. 9, 2014 and to U.S.Patent Application Ser. No. 62/183,522, filed on Jun. 23, 2015.

TECHNICAL FIELD

This present invention relates to additive manufacturing, also known as3D printing.

BACKGROUND

Additive manufacturing (AM), also known as solid freeform fabrication or3D printing, refers to any manufacturing process where three-dimensionalobjects are built up from raw material (generally powders, liquids,suspensions, or molten solids) in a series of two-dimensional layers orcross-sections. In contrast, traditional machining techniques involvesubtractive processes and produce objects that are cut out of a stockmaterial such as a block of wood, plastic or metal.

A variety of additive processes can be used in additive manufacturing.The various processes differ in the way layers are deposited to createthe finished objects and in the materials that are compatible for use ineach process. Some methods melt or soften material to produce layers,e.g., selective laser melting (SLM) or direct metal laser sintering(DMLS), selective laser sintering (SLS), fused deposition modeling(FDM), while others cure liquid materials using different technologies,e.g. stereolithography (SLA).

Sintering is a process of fusing small grains, e.g., powders, tocreating objects from smaller grains, e.g., powders using atomicdiffusion. Sintering usually involves heating a powder. The powder usedin sintering need not reach a liquid phase during the sintering process,in contrast to melting. When a powdered material is heated to atemperature below the melting point in a sintering process, the atoms inthe powder particles diffuse across the boundaries of the particles,fusing the particles together to form a solid piece. As the sinteringtemperature does not have to reach the melting point of the material,sintering is often used for materials with high melting points such astungsten and molybdenum.

Both sintering and melting can be used in additive manufacturing. Thematerial being used determines which process occurs. An amorphous solid,such as acrylonitrile butadiene styrene (ABS), is actually a supercooledviscous liquid, and does not actually melt; as melting involves a phasetransition from a solid to a liquid state. Thus, selective lasersintering (SLS) is the relevant process for ABS, while selective lasermelting (SLM) is used for crystalline and semi-crystalline materialssuch as nylon and metals, which have a discrete melting/freezingtemperature and undergo melting during the SLM process.

Conventional systems that use a laser beam as the energy source forsintering or melting a powdered material typically direct the laser beamon a selected point in a layer of the powdered material and selectivelyraster scan the laser beam to locations across the layer. Once all theselected locations on the first layer are sintered or melted, a newlayer of powdered material is deposited on top of the completed layerand the process is repeated layer by layer until the desired object isproduced. As the density of the finished object depends on the peaklaser power and not on the duration of the laser irradiation,conventional systems typically use a pulsed laser.

An electron beam can also be used as the energy source to causesintering or melting in a material. Once again, the electron beam needsto be raster scanned across the layer to complete the processing of aparticular layer.

SUMMARY

In one aspect, an additive manufacturing system includes a platen, afeed material dispenser apparatus configured to deliver a first feedmaterial onto the platen in a pattern specified by a computer aideddesign program to form a layer of the feed material on the platen, aheat source configured to apply heat to all of the layer of feedmaterial simultaneously; and a controller configured to cause the heatsource to raise a temperature of all of the layer of feed materialsimultaneously to a temperature sufficient to cause the first feedmaterial to fuse.

In another aspect an additive manufacturing system includes a platen, afeed material dispenser apparatus configured to deliver a first feedmaterial onto the platen in a pattern specified by a computer aideddesign program to form a layer of feed material on the platen, a heatsource configured to apply heat simultaneously to a region of the layerof feed material extending across a width of the platen and to scan theregion across a length of the platen; and a controller configured tocause the heat source to raise a temperature of the region of the layerof feed material simultaneously to a temperature sufficient to cause thefirst feed material to fuse.

In another aspect, an additive manufacturing system, the system includesa platen, a feed material delivery system configured to deliver feedmaterial to a location on the platen specified by a computer aideddesign program, and a heat source configured to raise a temperature ofthe feed material at two or more locations on the platen simultaneously.

In another aspect, a method of additive manufacturing includesdispensing a layer of feed material on a platen, the layer of feedmaterial including a first plurality of cells formed of a first feedmaterial and a second plurality of cells formed of a second feedmaterial. The first feed material has a first sintering or meltingtemperature and the second feed material has having a different secondsintering or melting temperature, and the method includes heating all ofthe layer of feed material simultaneously to a temperature above thefirst sintering or melting temperature and below the second sintering ormelting temperature.

In another aspect, a method of additive manufacturing includesdispensing a layer of feed material on a platen, the layer of feedmaterial including a first plurality of cells formed of a first feedmaterial and a second plurality of cells formed of a second feedmaterial. The first feed material has a first sintering or meltingtemperature and the second feed material has having a different secondsintering or melting temperature. The method includes simultaneouslyheating a region of the layer of feed material that extends across awidth of the platen to a temperature above the first sintering ormelting temperature and below the second sintering or meltingtemperature, and scanning the region across a length of the platen.

In another aspect, an additive manufacturing system includes a platen, afeed material dispenser apparatus configured to deliver a feed materialonto the platen in a pattern specified by a computer aided designprogram to form a layer of the feed material on the platen, and a plasmasource configured to generate an electrical potential in all of thelayer of feed material simultaneously, the electrical potential beingsufficient to cause fusing of the feed material.

In another aspect, an additive manufacturing system includes a platen, afeed material dispenser assembly configured to deliver a first feedmaterial over the platen in a pattern specified in a computer-readablemedium to form a layer of feed material over the platen, a heat sourceconfigured to apply heat to all of the layer of feed materialsimultaneously, and a controller configured to cause the heat source toraise a temperature of all of the layer of feed material simultaneouslyto a temperature sufficient to cause the first feed material to fuse.

In another aspect, a method of additive manufacturing includesdispensing a layer of a first feed material over a platen in a patternspecified in a computer-readable medium, and heating all of the layer offeed material simultaneously above a temperature at which the first feedmaterial fuses.

Implementations of either the above system or method can include one ormore of the following features.

The heat source may include an array of heat lamps configured to heatall of the layer simultaneously. The array of heat lamps may bepositioned directly above the platen. The heat source may include aplasma source. The plasma source may be configured to cause chargedparticles to bombard the layer of feed material. Th plasma source may beconfigured to generate an electrical potential in portions of the layerof feed material simultaneously, the electrical potential beingsufficient to cause fusing of the first feed material. The system mayinclude a secondary heat source configured to raise the layer of feedmaterial to a temperature below a temperature at which the first feedmaterial fuses. The secondary heat source may include a resistive heaterembedded in the platen. The controller may be configured to cause theheat source to apply heat to all of the layer of feed materialsimultaneously after the secondary heat source heats the layer of feedmaterial.

The feed material delivery system may include a first dispenserconfigured to dispense the first feed material and a second dispenserconfigured to dispense a second feed material, the layer of feedmaterial comprising the first material and the second material. Thefirst feed material may fuse at a first temperature and the second feedmaterial may fuse at a second temperature that is higher than the firsttemperature. The controller may be is configured to cause the heatsource to raise the temperature of the layer of feed materialsimultaneously to a temperature below the second temperature. The firstdispenser and the second dispenser may each include a gate that isindividually controllable and the gate may be configured to releaserespective first or second feed material at locations on the platenaccording to the pattern specified in the computer-readable medium. Thegate may be a piezoelectric printhead, a pneumatic valve, amicroelectromechanical systems (MEMS) valve, a solenoid valve or amagnetic valve. The system may include a second heat source in theplaten. The controller may be configured to cause the second heat sourceto maintain a base temperature of the platen at an elevated temperaturelower than both the first and second temperature.

The heat source may be positioned on a same side of the platen as thedispenser and be configured to apply radiant heat to all of the layersimultaneously. The heat source may be spaced from the platensufficiently for the dispenser to pass between the heat source and theplaten. The heat source may include an array of heat lamps configured toheat all of the layer simultaneously. The heat source may be positionedon a side of the platen farther from the dispenser. The heat source maybe embedded in the platen and be configured to apply conductive heat tothe layer.

The feed material delivery system may include a line of dispensersconfigured to deliver a line of feed material simultaneously. The lineof dispensers may be configured to be translated across the platen todeliver a layer of feed material. The feed material delivery system mayinclude a two dimensional array of dispensers configured to deliver allof the layer simultaneously. A piston may be configured to actuate theplaten vertically. The controller may be configured to cause the pistonto be lowered after a layer of feed material has been heated and priorto the feed material delivery system delivering a second layer of feedmaterial above the layer of feed material that has been heated.

In another aspect, an additive manufacturing system includes a platen, afeed material dispenser apparatus configured to deliver a first feedmaterial over the platen in a pattern specified in a computer-readablemedium to form a layer of feed material over the platen, a heat sourceconfigured to apply heat simultaneously to a region of the layer of feedmaterial extending across a width of the platen and to scan the regionacross a length of the platen, and a controller configured to cause theheat source to raise a temperature of the region of the layer of feedmaterial simultaneously to a temperature sufficient to cause the firstfeed material to fuse.

In another aspect, a method of additive manufacturing includesdispensing a layer of feed material over a platen in a pattern specifiedin a computer-readable medium, simultaneously heating a region of thelayer of feed material that extends across a width of the platen to atemperature above the first sintering or melting temperature and belowthe second sintering or melting temperature, and scanning the regionacross a length of the platen.

Implementations of either the above system or method can include one ormore of the following features.

The region may be substantially linear, and the heat source may beconfigured to scan the region in a direction perpendicular to a primaryaxis of the region. The heat source may include a laser to generate alaser beam and optics may receive the laser beam and expand a crosssection of the laser beam along the width of the platen. The optics mayinclude a beam expander and a cylindrical lens. A mirror galvanometer tocause the region to scan across the length of the platen. The heatsource may include a linear array of heat lamps. An actuator may becoupled to at least one of the heat source or platen to cause the regionto scan across the length of the platen. A secondary heat source may beconfigured to raise the layer of feed material to a temperature below atemperature at which the first feed material fuses. The secondary heatsource may include a resistive heater embedded in the platen.

The feed material delivery system may include a first dispenserconfigured to dispense the first feed material and a second dispenserconfigured to dispense a second feed material, so that the layer of feedmaterial includes the first material and the second material. The firstfeed material may fuses at a first temperature and the second feedmaterial may fuses at a second temperature higher than the firsttemperature. The controller may be configured to cause the heat sourceto raise the temperature of the layer of feed material simultaneously toa temperature below the second temperature. A second heat source may belocated in the platen, and the controller may be configured to cause thesecond heat source to maintain a base temperature of the platen at anelevated temperature lower than both the first and second temperature.

In another aspect, an additive manufacturing system includes a platen, afeed material dispenser apparatus configured to deliver a first feedmaterial over the platen, and a plasma source configured to generate aplasma that causes fusing of the first feed material.

In another aspect, a method of additive manufacturing includesdispensing a layer of feed material over a platen, and generating aplasma that causes fusing of the first feed material.

Implementations of either the above system or method can include one ormore of the following features.

The plasma source may include two electrodes and a power source tosupply a radio frequency voltage to at least one of the two electrodes.A first electrode of the two electrodes may be in or on the platen. Asecond electrode of the two electrodes may be suspended above theplaten. The power supply may be configured to supply a radio frequencyvoltages having a first frequency to one of the two electrodes, and tosupply a radio frequency voltage having a second frequency to the otherone of the two electrodes, with the first frequency different from thesecond frequency.

The platen may be supported in a chamber, e.g., a vacuum chamber. A gasinlet may be configured to introduce a gas into the chamber. The gas maybe configured to form ions, and the power source may be configured drivethe electrodes at a power and frequency such that the ions are caused tobe embedded into the layer.

The plasma source may be configured to generate a plasma that extendsacross the platen and raise all of the layer of feed materialsimultaneously to a temperature sufficient to cause the first feedmaterial to fuse. The dispenser may be configured to deliver the firstfeed material in a pattern specified in a computer-readable medium.

The feed material delivery system may include a first dispenserconfigured to dispense the first feed material and a second dispenserconfigured to dispense a second feed material, so that the layer of feedmaterial includes the first material and the second material. The firstfeed material may fuse at a first temperature and the second feedmaterial may fuses at a second temperature that is higher than the firsttemperature. The plasma source may be configured to generate plasma thatdoes not cause fusing of the second feed material. A second heat sourcemay be configured raise the layer of feed material to an elevatedtemperature lower than both the first and second temperature.

In another aspect, an additive manufacturing system includes a platen, afeed material dispenser apparatus to dispense a layer of feed materialover the platen, a heat source, and a controller. The feed materialdispenser apparatus includes a first dispenser configured to dispense afirst feed material and a second dispenser configured to dispense asecond feed material, such that the layer of feed material comprises thefirst feed material and the second feed material. The first feedmaterial may fuses at a first temperature and the second feed materialmay fuses at a higher second temperature. The a heat source may beconfigured to heat to the layer of feed material to a temperaturesufficient to cause the first feed material to fuse but insufficient tocause the second feed material to fuse. The controller may be configuredto cause the dispenser to dispense the first feed material in a patternspecified in a computer-readable medium.

Implementations may include one or more of the following features. Thecontroller may be configured to cause the feed material dispenser todispense one of either the first feed material or the second configuredat each voxel in the layer of feed material. The heat source may beconfigured to heat all of the layer of feed material to the temperaturesimultaneously. The first dispenser and the second dispenser may eachinclude a gate that is individually controllable, and the gate may beconfigured to release respective first or second feed material atlocations on the platen according to the pattern specified in thecomputer-readable medium. The gate may include an element selected fromthe group consisting of a piezoelectric printhead, a pneumatic valve, amicroelectromechanical systems (MEMS) valve, a solenoid valve and amagnetic valve.

In another aspect, an additive manufacturing system includes a platen, afeed material dispenser apparatus to dispense a layer of feed materialover the platen, a heat source and a controller. The feed materialdispenser apparatus includes a first dispenser configured to dispense afirst feed material and a second dispenser configured to dispense asecond feed material, such that the layer of feed material comprises thefirst feed material and the second feed material. The first feedmaterial fuses at a first temperature and the second feed material fusesat a higher second temperature. The heat source is configured to applyheat to all of the layer of feed material simultaneously. The controlleris configured to cause the dispenser to dispense the first feed materialin a pattern specified in a computer-readable medium and to cause theheat source to raise a temperature of all of the layer of feed materialsimultaneously to a temperature above the first temperature and belowthe second temperature.

In another aspect, a method of additive manufacturing includesdispensing a layer of feed material on a platen, the layer of feedmaterial including a first plurality of cells formed of a first feedmaterial and a second plurality of cells formed of a second feedmaterial, wherein the first feed material fuses at a first temperatureand the second feed material fuses at a different second temperature,and heating all of the layer of feed material simultaneously to atemperature above the first temperature and below the secondtemperature.

Implementations can provide one or more of the following advantages. Thenumber and size of thermal fluctuations experience by the material canbe reduced. Material properties of the fabricated object can be morespatially uniform. The time needed to fabricate an object can bereduced. For example, for a cube having a length L, the time needed tofabricate the cube can scale as L or L² rather than L³.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other aspects,features, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic view of an additive manufacturing system.

FIG. 1B is a schematic view of the additive manufacturing system after afew layers of material have been fabricated.

FIG. 2A is a schematic view of a point dispenser.

FIG. 2B is a schematic view of a line dispenser.

FIG. 2C is a schematic view of an array dispenser.

FIG. 2D is a schematic of a through-silicon-via in two different modesof operation.

FIG. 3A is a schematic view of an additive manufacturing system.

FIG. 3B is a schematic view of a particle on a cathode.

FIG. 3C is a schematic view of driving pulse sequence. Like referencesymbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A point on a layer of a powdered material that is being sintered ormelted by a pulsed laser beam experiences a series of abrupt temperaturefluctuations as the laser beam delivers energy to locations in thevicinity of that point during raster scanning. When a new layer ofpowdered material is deposited over a completed layer, the same point onthe completed layer experiences another series of abrupt temperaturefluctuation as heat deposited by the pulsed laser beam is conducted fromthe top layer to the completed layer. Such temperature fluctuations cancause changes in temperature of more than 1500° C. at a particular pointin the layer and can repeat every 2-3 second, depending on the scan rateof the laser beam.

The large temperature fluctuations caused by the point-by-pointsintering or melting of a powdered material can create thermal stresseswithin the printed object. Furthermore, material properties, such as thegrain size of the sintered material may vary due to variations in thethermal history at different locations in the finished object. Forexample, the increase in temperature may cause localized regions of thesintered or melted portion to recrystallize and form a region that has adifferent grain size from a neighboring region. In order to obtain morerepeatable material properties in the fabricated object, better controlof grain size is desired.

The time needed to fabricate objects using point-to-point sintering ormelting techniques scales with the third power of a linear dimension ofthe object. For example, for a cube having a length L, the time neededto fabricate the cube would scale as L³.

FIG. 1A shows a schematic of an exemplary additive manufacturing system100. The system 100 includes and is enclosed by a housing 102. Thehousing 102 can, for example, allow a vacuum environment to bemaintained in a chamber 103 inside the housing, but alternatively theinterior of the chamber 103 can be a substantially pure gas or mixtureof gases, e.g., a gas or mixture of gases that has been filtered toremove particulates, or the chamber can be vented to atmosphere. Thevacuum environment or the filtered gas can reduce defects duringmanufacture of a part. For some implementations, the chamber 103 can bemaintained at a positive pressure, i.e., above atmospheric pressure.This can help prevent the external atmosphere from entering the chamber103.

The additive manufacturing system 100 includes a material dispenserassembly 104 positioned above a platen 120. A vertical position of theplaten 120 can be controlled by a piston 132. After each layer of powderhas been dispensed and fused, the piston 132 can lower the platen 120and any layers of powder thereon, by the thickness of one layer, so thatthe assembly is ready to receive a new layer of powder.

The platen 120 can be sufficiently large to accommodate fabrication oflarge-scale industrial parts. For example, the platen 120 can be atleast 500 mm across, e.g., 500 mm by 500 mm square. For example, theplaten can be at least 1 meter across, e.g., 1 meter square.

A controller 140 controls a drive system (not shown), e.g., a linearactuator, connected to the dispenser assembly 104. The drive system isconfigured such that, during operation, the dispenser assembly ismovable back and forth parallel to the top surface of the platen 120(along the direction indicated by arrow 106). For example, the dispenserassembly 104 can be supported on a rail that extends across the chamber103. Alternatively, the dispenser assembly 104 could be held in a fixedposition, while the platen 120 is moved by the drive system. As thedispenser assembly 104 scans across the platen, the dispenser assembly104 deposits feed materials at an appropriate location on the platen120. The dispenser assembly 104 can store and dispense two or moredifferent feed materials. The dispenser assembly includes a firstdispenser 104 a having a first reservoir 108 a to hold first feedmaterial 114 a, and a second dispenser 104 b having a second reservoir108 b to hold a second feed material 114 b. Release of the first feedmaterial 114 a and second feed material 114 b is controlled by a firstgate 112 a and a second gate 112 b, respectively. Gates 112 a and 112 bare controlled independently so that one of the two feed materials isdeposited at a particular location on the platen 120.

The controller 140 directs the dispenser assembly 104 to deposit eitherthe first feed material 114 a or the second feed material 114 b atlocations on the platen according to a printing pattern that can bestored in non-transitory computer-readable medium. For example, theprinting pattern can be stored as a file, e.g., a computer aided design(CAD)-compatible file, that is then read by a processor associated withthe controller 140. Electronic control signals are then sent to thegates 112 a and 112 b to dispense the respective feed material when therespective dispensers 104 a and 104 b are translated to a positionspecified by the CAD-compatible file.

In some implementations, each dispenser 104 a, 104 b includes aplurality of openings through which feed material can be dispensed. Eachopening can have an independently controllable gate, so that delivery ofthe feed material through each opening can be independently controlled.

In some implementations, the plurality of openings extend across thewidth of the platen, e.g., in direction perpendicular to the directionof travel 106 of the dispensers 104 a, 104 b. In this case, inoperation, the dispensers 104 a, 104 b can scan across the platen 120 ina single sweep in the direction 106. In some implementations, foralternating layers the dispensers 104 a, 104 b can scan across theplaten 120 in alternating directions, e.g., a first sweep in thedirection 106 and a second sweep in the opposite direction.

Alternatively, e.g., where the plurality of openings do not extendacross the width of the platen, the dispensing system 104 can beconfigured such that the dispensers 104 a, 104 b move in two directionsto scan across the platen 120, e.g., a raster scan across the platen120, to deliver the material for a layer.

The gates 112 a, 112 b of the dispensers 104 a, 104 b can be provided bya piezoelectric printhead, and/or one or more of pneumatic valves,microelectromechanical systems (MEMS) valves, solenoid valves, ormagnetic valves, to control the release of feed material from the eachdispenser 104 a, 104 b. The dispensers 104 a, 104 b can deposit aselected feed material at selected locations on the platen 120. Thehigher the spatial resolution of the voxels, the smaller the volume ofthe voxels and thus the lower the quantity of feed material that wouldbe dispensed per voxel.

The feed material can be dry powders of metallic or ceramic particles,metallic or ceramic powders in liquid suspension, or a slurry suspensionof a material. For example, for a dispenser that uses a piezoelectricprinthead, the feed material would typically be particles in a liquidsuspension. For example, either or both dispensers 104 a, 104 b candeliver their powder in a carrier fluid, e.g. a high vapor pressurecarrier, e.g., Isopropyl Alcohol (IPA), ethanol, orN-Methyl-2-pyrrolidone (NMP), to form the layers of powder material. Thecarrier fluid can evaporate prior to the sintering step for the layer.Alternatively, a dry dispensing mechanism, e.g., an array of nozzlesassisted by ultrasonic agitation and pressurized inert gas, can beemployed to dispense the first particles.

Examples of metallic particles include metals, alloys and intermetallicalloys. Examples of materials for the metallic particles includetitanium, stainless steel, nickel, cobalt, chromium, vanadium, andvarious alloys or intermetallic alloys of these metals. Examples ofceramic materials include metal oxide, such as ceria, alumina, silica,aluminum nitride, silicon nitride, silicon carbide, or a combination ofthese materials.

Optionally, the system 100 can include a compaction and/or levellingmechanism to compact and/or smooth the layer of feed materials depositedover the platen 120. For example, the system can include a roller orblade that is movable parallel to the platen surface by a drive system,e.g., a linear actuator. The height of the roller or blade relative tothe platen 120 is set to compact and/or smooth the outermost layer offeed material. The roller can rotate as it translates across the platen.

During manufacturing, layers of feed materials are progressivelydeposited and sintered or melted. For example, the first and second feedmaterials 114 a and 114 b are dispensed from the dispenser assembly 104to form a first layer 152 that contacts the platen 120, as shown in FIG.1B. Subsequently deposited layers of feed material can form additionallayers, e.g., layers 154 and 156, each of which is supported on anunderlying layer, e.g., layer 154 and 152, respectively.

After each layer is deposited, the outermost layer is processed to causeat least some of the layer to fuse, e.g., by sintering or by melting andresolidifying.

The second feed material 114 b can have a higher sintering or meltingpoint than the first feed material 114 a. For example, the temperaturedifference in melting point between the first feed material 114 a andthe second feed material 114 b may be greater than 200° C.

The system 100 includes a heat source 134 configured to raise thetemperature of an entire deposited layer simultaneously. In operation,the heat source 134 raises the temperature of the whole outermost layer156 to a temperature that is above a first temperature at which thefirst feed material 114 a fuses, but below above a second temperature atwhich the second feed material 114 b fuses. Consequently, a depositedcluster of the first feed material 114 a can melt and thus fuse togetherto form fused material 160, whereas the second feed material 114 bremains in loose (e.g., powder) form. The heat source 134 can be aradiative heater. For example, the heat source 134 can be atwo-dimensional array of heat lamps 136.

The heat source 134 can be triggered after each layer has been depositedby the dispensing system 104. In contrast to a point-by-point rasterscan, in which the time needed to fuse the material in an object scalesas L³, the time needed to fuse the material in the object using system100 scales with L, the thickness (i.e., the number of layers) of theobject. This permits a significant increase in throughput, and may makeadditive manufacturing economically feasible over a wider range ofproducts or at larger sizes.

As illustrated in FIGS. 1A and 1B, the heat source 134 can be positioned“above” the platen, i.e., on the same side of the platen 120 on whichthe feed material is deposited, and spaced away sufficiently from theplaten 120 so that the dispensers 104 a, 104 b can pass between theplaten 120 and the heat source 134. As shown in FIGS. 1A and 1B, thearray of heat lamps 136 is disposed directly above the platen 120, andthe heat lamps 136 are arranged in a plane parallel to the surface ofthe platen 120 with the individual lamps oriented perpendicular to theplaten surface. However, the heat lamps 136 could be above the platenbut partially or entirely off to the lateral sides of the platen, withthe lamps oriented at angle such that the heat radiation is at anon-zero angle of incidence on the layer of feed material on the platen.

In some implementations the heat source 134 could be positioned “below”the platen, i.e., on the side of the platen 120 opposite the surface onwhich the feed material is deposited. However, having the heat source134 above the platen is advantageous in that the heat can be deliveredprimarily to the outermost layer, e.g., layer 156, rather thantransmitting heat to the platen and underlying layers 152, 154.

A secondary heat source can be used to raise the temperature of thelayer of feed material(s) to a temperature below the temperature atwhich the first feed material fuses. In general, the secondary heatsource applies heat to the outermost layer 156 of feed material beforethe heat source 134. For example, the secondary heat source could beoperated continuously, e.g., while the layer is being deposited. Forexample, the platen 120 can be heated by an embedded heater 126 to abase temperature that is below the melting points of both the first andsecond feed materials. As another example, additional heat lamps couldprovide the secondary heat source.

The heat source 134 is triggered to impart sufficient energy to sinteror melt the first feed material without sintering or melting the secondfeed material. In this way, the heat source 134 can be configured toprovide a smaller temperature increase to the deposited material toselectively melt the first feed material. Transitioning through a smalltemperature difference can enable each deposited layer of feed materialsto be processed more quickly. Transitioning through a small temperaturedifference can also reduce thermal stress and thus improve quality ofthe fabricated object. For example, the base temperature of the platen120 can be about 500-1700° C., e.g., 1500° C., and the heat source 134can be triggered to impart energy to cause a temperature increase ofabout 50° C.

For example, considering the case of titanium, which has a melting pointof 1668° C., heat of fusion of 14.15 kJ/mol, a molar heat capacity of25.06 J/mol/K and a density of 4.506 g/cm³. Assuming the feed materialis titanium spheres having a diameter of 10 microns, the energy neededto raise one titanium sphere by 50° C. and melt it is ˜0.7 μJ. Assumingheating a square area having sides of 10 cm on the platen 120 for 1second using the heat lamps each time they are used to melt a layerhaving a thickness of a single sphere, the array of heat lamps 136 canhave a power rating of at least ˜75 W, assuming all the energy from theheat lamps is absorbed by the titanium spheres. In other words,reflection and scattering of the thermal radiation from the heater lampshave not been taken into account above.

In contrast, without the base temperature of the platen been maintainedat, for example, 50° C. below the melting point of the first feedmaterial, the power rating of the array 134 would have to be at least˜270 W to raise the temperature of the first feed material from roomtemperature to the melting point of the material and to melt thematerial.

Alternatively, the heat source 134 could be used to heat the platen 120to the base temperature, and the embedded heater 126 could be triggeredto impart sufficient energy to melt the first feed material withoutmelting the second feed material. However, having the heat source 134 betriggered is advantageous in that the change in temperature can occurprimarily in the outermost layer, e.g., layer 156, rather than having topropagate through the platen and underlying layers 152, 154.

As shown in FIG. 1B, the platen 120 can include side walls 122 and 124that are each heated by heaters 128 and 130, respectively.

In some implementations, rather than the heat source 134 can beconfigured to raise the temperature of a generally linear region thatextends across the platen. The heated region can be scanned linearlyacross the platen, e.g., in a direction perpendicular to the primaryaxis of the linear region (i.e., assuming the length is greater than thewidth, the primary axis is the length direction). In such a system, thetime needed to fuse the material in an object scales as L² rather thanL³. The heat source 134 can include a laser beam that is appropriatelyshaped, for example, using cylindrical lenses, to achieve a line shape.When a line of laser beam is used, the laser beam would be scannedacross the platen to cover an entire layer of deposited feed material.Alternatively or in addition, the heat source 134 could include a lineararray of heat lamps.

Relative motion of the linear region heated by the heat source 134across the outermost layer of feed material can be accomplished byholding the platen 120 fixed while the heat source 134 moves, e.g., witha linear actuator, by holding the heat source 134 stationary while theplaten 120 moves, e.g., with a linear actuator, or by scanning the beamgenerated by the heat source, e.g., by a mirror galvanometer.

In operation, after each layer has been deposited and heat treated, theplaten 120 is lowered by an amount substantially equal to the thicknessof layer. Then the dispenser assembly 104, which does not need to betranslated in the vertical direction, scans horizontally across theplaten to deposit a new layer that overlays the previously depositedlayer, and the new layer can then be heat treated to fuse the first feedmaterial. This process can be repeated until the full 3-dimensionalobject is fabricated. The fused material 160 derived by heat treatmentof the first feed material provides the additively manufactured object,and the loose second feed material 114 b can be removed and cleaned offafter the object is formed.

As noted above, the first feed material 114 a and the second feedmaterial 114 b are deposited in each layer by the dispenser assembly 104in a pattern stored in a 3D drawing computer program controlled by thecontroller 140. For some implementations, the controller 140 controlsthe dispenser assembly 104 so that each voxel in a layer is filled byone of the feed materials, e.g., there are no empty voxels. For example,assuming that two feed materials are used, any voxel in to which thefirst dispenser 104 a does not deliver the first feed material 114 a,the second dispenser 104 b will deliver the second feed material 114 b.This can ensure that each voxel in subsequently dispensed layers will besupported by an underlying material.

Using a heat source that raises the temperature of the entire layersimultaneously, e.g., 2-dimensional array of heater lamps, allowslayerwise heating of the feed materials, speeding up the fabricationprocess. In addition, the entire layer of feed material is exposed tothe heat from the array of heater lamps at the same time, which canprovide better control to the thermal history across the layer. Inparticular, the number of fluctuations of temperature experienced by aparticular point in the layer can be reduced. As a result, bettercontrol of grain sizes of the fused material can be achieved.

As shown in FIG. 2A, a dispenser 204, which could be used for thedispenser 104 a and/or 104 b, may be a single point dispenser and thedispenser would be translated across the x and y direction of the platen210 to deposit a complete layer of feed material 206, which can be feedmaterial 114 a and/or feed material 114 b, on the platen 210.

Alternatively, as shown in FIG. 2B, a dispenser 214, which could be usedfor the dispenser 104 a and/or 104 b, can be a line dispenser thatextends across the width of the platen. For example, the dispenser 214could include a linear array of individually controllable openings,e.g., nozzles. The dispenser 214 can be translated only along onedimension to deposit a complete layer of feed material on the platen.

Alternatively, as shown in FIG. 1C, a dispenser 224, which could be usedfor the dispenser 104 a and/or 104 b, includes a two-dimensional arrayof individually controllable openings, e.g., nozzles. For example, thedispenser 224 can be a large area voxel nozzle print (LAVoN). LAVoN 224allows a complete two dimensional layer of feed material to be depositedsimultaneously. LAVoN 224 may be a dense grid of through-silicon via(TSV) 228 formed in bulk silicon 226. Each TSV 228 can be controlled bya piezoelectric gate 230 that closes an exit opening of a particular 228when an appropriate voltage is applied such that the feed material 206is retained within the TSV. When a different voltage is applied to theTSV 228, the piezoelectric gate 230 can open an exit opening of aparticular TSV 228, allowing feed material to be deposited on a platen.Each of the TSV 228 in the LAVoN 224 is individually accessed by controlsignals produced from a controller based on a CAD-file that defines thefabricated object. LAVoN 224 can be used to deposit a single feedmaterial only. In such a case, no feed material is deposited at regionsof void in the fabricated object or in regions beyond the fabricateobject. Alternatively, each “pixel” of the LAVoN 224 can be served bytwo TSV 228, each holding one of the two types of feed material. Whenthe TSV 228 for one feed material is turned on, the TSV 228 for theother feed material at that pixel is turned off. The embodiments shownin FIGS. 2B-2D would speed up the deposition process of the feedmaterial on the platen.

As an alternative or in addition to the radiative and/or conductive heatsources described for the implementations of FIGS. 1A and 1B, plasmabased systems can also be used to achieve layer-wise fusing of feedmaterials. As shown in FIG. 3A, an additive manufacturing system 300 issimilar to the additive manufacturing system 100 of FIGS. 1A and 1B, butincludes a plasma generation system 302, which provides a plasma source.The additive manufacturing system 300 includes chamber walls 304 thatdefine the chamber 103.

The plasma generation system 302 includes an electrode 310, i.e., afirst electrode. The electrode 310 can be a conductive layer on or inthe platen 120. This permits the electrode 310 to can be translatedvertically, similar to the piston 132 in FIGS. 1A and 1B. The electrode310 can serve as the anode.

The additive manufacturing system 300 also include a counter-electrode312, i.e., as second electrode. The counter-electrode 312 can serve asan anode. Although FIG. 3A illustrates the counter-electrode 312 as aplate suspended in the chamber 103, the counter-electrode 312 could haveother shapes or be provided by portions of the chamber walls 304.

At least one of the electrode 310 and/or counter-electrode 312 isconnected to an RF power supply, e.g., an RF voltage source. Forexample, the electrode 310 can be connected to an RF power supply 320and the counter-electrode can be connected to an RF power supply 322. Insome implementations, one of the electrode 310 or counter-electrode 312is connected to an RF power supply and the other of the electrode 310 orcounter-electrode 312 is grounded or connected to an impedance matchingnetwork.

By application of an RF signal of appropriate power and frequency, aplasma 340 forms in a discharge space 342 between the electrode 310 andthe counter-electrode 312. A plasma is an electrically neutral medium ofpositive and negative particles (i.e. the overall charge of a plasma isroughly zero). The plasma 340 is depicted as elliptical only forillustrative purposes. In general, the plasma fills the region betweenthe electrode 310 and the counter-electrode 312, excluding a “dead zone”near the anode surface.

Optionally, the system 300 can include a magnet assembly 350 which cancreate a magnetic field of, for example, 50 Gauss to 400 Gauss. Themagnet assembly 350 can include a permanent magnet in the platen 120,e.g., located near a top surface 314 of the platen 120. Alternatively,the magnet assembly can include an electromagnet, e.g., an antenna coilwound about the exterior surface of a dielectric (e.g., quartz) portionof the walls 304 of the vacuum chamber 103. An RF current is passedthrough the antenna coil. When operated in a resonance mode with theapplied RF power, the antenna coil generates an axial magnetic fieldwithin the chamber 103. The magnetic field can confine chargedparticles, e.g., negative particles such as electrons, to a helicalmotion.

The chamber 103 defined by the chamber walls 304 can be enclosed in thehousing 102. The chamber walls 304 can, for example, allow a vacuumenvironment to be maintained in a chamber 103 inside the housing 102. Avacuum pump in the housing 102 can be connected to the chamber 103 by avacuum vent 306 to exhaust gases from within the chamber 103. Processgases, such as argon and helium, which are non-reactive, can beintroduced into the chamber 103 via a gas inlet 308. Depending on theprocesses, different gases can be introduced to the chamber 103. Forexample, oxygen can be introduced to cause chemical reactions.

A dispenser assembly 104, similar to the one shown in FIGS. 1A and 1B,or in alternative forms as those shown in FIGS. 2A-2C, can be used todeposit feed materials 114 a and 114 b over the platen 120. Thecontroller 140 similarly controls a drive system (not shown), e.g., alinear actuator, connected to the dispenser assembly 104. The drivesystem is configured such that, during operation, the dispenser assemblyis movable back and forth parallel to the top surface of the platen 120.

The left side of FIG. 3B shows a profile 362 (exaggerated, not to scale)of a particle 360 of the feed material 114 a. The particle 360 is inpoint contact with the top surface 314 of the electrode 310 or apreviously deposited conductive underlying layer that is on the platen120. In short, with “point contact”, due to surface roughness and/orcurvature of the particle, only a limited surface area of the particlecontacts the top surface 314.

Without being limited to any particular theory, upon applying RF poweron the electrode 310 to produce the plasma 340, parts of the particle360 that are not in direct contact with the top surface 314 canexperience a large voltage, e.g., due to plasma bias. The feed materialneed not be non-metallic or non-conductive to experience the largevoltage due to the plasma bias. In the case of a metallic particleconductivity decreases as cross-section decreases. Thus, the pointcontact basically acts as a resistor for a metallic particle.

Again without being limited to any particular theory, localized arcingacross a gap 366 between the particle 360 and either the electrode 310or underlying conductive layer can cause fusing, e.g., melting orsintering to occur. In general, a larger gap causes a smaller the amountof arcing, for a given voltage differential between the cathode and theparticle. Even though the arcing/melting is localized to regions of theparticles that are not in direct contact with the cathode, the heatgenerated by the arcing is sufficient to fuse the material, e.g., bymelting the entire particle 360 or sintering of the particle 360 toadjacent particles.

In general, there exists enough curvature (in some (e.g., all) of theparticles of the first feed material 114 a for arcing to occur. Thus,the particles need not be oriented to be deposited on the cathode in aparticular way. The second feed material 114 b, which is not fused inthe part to be additively manufactured, has a much higher melting pointsuch that even arcing in the plasma would not lead to melting or fusingof the first feed material 114 a. For example, the temperaturedifference in melting point between the first feed material 114 a andthe second feed material 114 b may be greater than 200° C.

The right side of FIG. 3B shows a profile 363 of the particle 360 afterit has been fused/melting by localized arcing into a fused particle 361.After fusing, gaps between the particle 361 and the top surface 314 arereduced (e.g., eliminated) to such an extent that local arcing no longeroccurs in the fused particle 361.

It should be understood that the above explanation is not limiting. Itmay be that heating of the layer of feed material is partially or entiredue to heat transfer from the plasma, e.g., due to kinetic bombardment.

As described in reference to FIGS. 1A and 1B, the dispenser assembly 104deposits either the first feed material 114 a or the second feedmaterial 114 b at locations over the platen 120 according to a printingpattern that can be stored as a computer aided design (CAD)-compatiblefile that is then read by a computer associated with the controller 140.

While FIG. 3B shows only a single particle on the electrode 310 forillustration purposes, in practice, an entire layer of feed material isdeposited over the platen 120 before the plasma 340 is formed in thesystem 300. For example, the plasma formation may be timed to a drivepulse 370, as shown in FIG. 3C, that is applied to control a supply ofpower to the electrode 310 and/or the counter-electrode 330.

During an on-state 372 of the drive pulse 370, the plasma 340 is formedbetween the electrode and the counter-electrode 330, and localizedfusing/melting occurs in the deposited first feed material 114 a. Duringthe off-state 374 of the drive pulse 370, the plasma 340 is not formedand the dispenser assembly 104 can be translated across the platen 120to deposit a new layer of feed material to be processed by the plasma340. The on-state and the off-state can last, for example, 0.5 seconds.

Similar to the system 100, the system 300 also processes the feedmaterials 114 a and 114 b one layer at a time, allowing processing timeto scale with L. When a new layer of feed material is deposited on topof a layer of feed material that has been fused/melted, the localizedarcing/melting that occurs on the top layer of feed material does notinfluence the underlying processed or fused/melted layers of feedmaterial. The platen 120 can be lowered after each layer has beenprocessed and fused such that the dispenser assembly 104 need not betranslated vertically.

Operating the system 300 under a vacuum environment may provide qualitycontrol for the material formed from processes occurring in the system300. Nonetheless, in some implementations the plasma 340 can also beproduced under atmospheric pressure.

A higher frequency (e.g., more than 50 MHz) drive voltage can be appliedto one of the electrodes (either the cathode or the anode), while alower frequency (e.g., less than 20 MHz) bias voltage can be applied tothe other electrode. In general, the higher frequency signal creates theflux of plasma. A higher frequency RF drive voltage creates a higherflux (i.e., more ions and electrons in the plasma). The lower frequencyRF bias voltage controls the energy of the ions in the plasma. At lowenough frequencies (e.g., 2 MHz), the bias signal can cause the ions inthe plasma to have enough energy to vaporize a feed material (e.g.,aluminum powder) that is deposited on a substrate (e.g., silicon wafer).In contrast, at a higher frequency bias signal (e.g., 13 MHz), meltingof the feed material can occur. Varying the RF frequency and point ofapplication would cause different melting performance of the feedmaterial. Melting performance can determine the recrystallization of thefeed material, which could lead to different stresses within the metaland different relaxation behavior.

The use of plasma to cause a temperature jump in a layer of feedmaterial also enables layer characteristics of the feed material to beeasily controlled. For example, the layer of feed material can be dopedby selectively implanting ions from the plasma. The doping concentrationcan be varied layer by layer. The implantation of ions can help releasepoint stress in the layer of feed material. Examples of dopants includephosphorous.

Indeed, the plasma can be biased such that gaps between the powderparticles of the feed material and the electrode cause a sufficientlylarge voltage to be developed on the powder, causing electron or ionbombardment on the feed material. The electrons or ions used in thebombardment can come from the plasma, and be accelerated to the feedmaterial when either a DC or an AC bias is applied on the feed material.Bombardment can be used to treat a layer, to etch material, tochemically alter (e.g., in reactive ion etch) the feed material, to dopethe feed material (e.g., to add a nitride layer), or be used for surfacetreatment.

Referring to either FIGS. 1A or 3A, the controller 140 of system 100 or300 is connected to the various components of the system, e.g.,actuators, valves, and voltage sources, to generate signals to thosecomponents and coordinate the operation and cause the system to carryout the various functional operations or sequence of steps describedabove. The controller can be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware. For example,the controller can include a processor to execute a computer program asstored in a computer program product, e.g., in a non-transitory machinereadable storage medium. Such a computer program (also known as aprogram, software, software application, or code) can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as a standaloneprogram or as a module, component, subroutine, or other unit suitablefor use in a computing environment.

As noted above, the controller 140 can include non-transitory computerreadable medium to store a data object, e.g., a computer aided design(CAD)-compatible file, that identifies the pattern in which the feedmaterial should be deposited for each layer. For example, the dataobject could be a STL-formatted file, a 3D Manufacturing Format (3MF)file, or an Additive Manufacturing File Format (AMF) file. For example,the controller could receive the data object from a remote computer. Aprocessor in the controller 140, e.g., as controlled by firmware orsoftware, can interpret the data object received from the computer togenerate the set of signals necessary to control the components of thesystem to print the specified pattern for each layer.

The processing conditions for additive manufacturing of metals andceramics are significantly different than those for plastics. Forexample, in general, metals and ceramics require significantly higherprocessing temperatures. For example, metals need to processed attemperature on the order of 400° C. or higher, e.g., 700° C. foraluminum. In addition, processing of metal should occur in vacuumenvironment, e.g., to prevent oxidation. Thus 3D printing techniques forplastic may not be applicable to metal or ceramic processing andequipment may not be equivalent. In addition, the fabrication conditionsfor large scale-industrial parts can be significantly more stringent.

However, some techniques described here could be applicable to plasticpowders. Examples of plastic powders include nylon, acrylonitrilebutadiene styrene (ABS), polyurethane, acrylate, epoxy, polyetherimide,polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polystyreneor polyamides.

Certain features that are described in the context of separateembodiments can also be implemented in combination in a singleembodiment, and conversely, various features that are described in thecontext of a single embodiment can also be implemented singly withoutthe other features of that embodiment.

For example, although the description above has focused on the use ofmultiple feed materials having different temperatures, the technique ofraising the temperature of the entire layer or raising the temperatureof a linear region that scans across the platen, either by radiated heator plasma, can be applied even if just a single feed material is beingused in each layer. In this case, only a single dispenser assembly isneeded. In addition, the controller can cause the dispenser assembly 104to deliver the single feed material to desired voxels over the platen120. The object being fabricated can be subject to certain constraints,e.g., each voxel of feed material in a new layer would be deposited onlyover voxels in the underlying layer where material was delivered.

As another example, although the description above has focused onraising the temperature of the entire layer or raising the temperatureof a linear region that scans across the platen, the technique ofdispensing multiple feed materials could be used with a heat source thatscans across the layer of material to controllably apply heat on avoxel-by-voxel basis. For example, the heat source can be a laser thatgenerates a laser beam that scans across the platen and has an intensitythat is modulated to control which voxels are fused. Relative motion ofthe region heated by the heat source can be provided by holding theplaten 120 fixed while the heat source 134 moves, e.g., with a pair oflinear actuators, by holding the heat source 134 stationary while theplaten 120 moves, e.g., with a pair of linear actuators, or by scanningthe beam generated by the heat source, e.g., by a mirror galvanometer.

As another example, although the description above has focused onapplying plasma to the entire layer of feed material, plasma could begenerated in an area that is smaller than the layer of feed material.For example, the area in which the plasma is generated can be sized tocontrol fusing of a region the layer of feed material, e.g., a singlevoxel, a region of multiple voxels that does not span the platen, or anelongated region that spans the width of the platen. This region can bescanned across the platen. The region affected by the plasma can becontrolled by appropriate configuration of the electrodes, e.g., acounter-electrode of appropriate size can be placed in proximity to theplaten. Where voxel-by-voxel control is possible, a continuous layer ofa single feed material can be dispensed over the platen, and the plasmacan be used to determine whether a particular voxel is fused. Relativemotion of the volume in which plasma is generated can be provided byholding the platen 120 fixed while the counter-electrode moves, e.g.,with a pair of linear actuators, or by holding the counter-electrodestationary while the platen 120 moves, e.g., with a pair of linearactuators.

As another example, the radiative heat source 134, e.g., an array ofheat lamps 135, and the plasma generation system 302 have been describedabove as part of separate implementations, some implementations caninclude both the radiative heat source 134 and the plasma generationsystem 302.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

1. An additive manufacturing system comprising: a platen; a feedmaterial dispenser assembly configured to deliver a first feed materialover the platen in a pattern specified in a computer-readable medium toform a layer of feed material over the platen; a heat source configuredto apply heat to all of the layer of feed material simultaneously; and acontroller configured to cause the heat source to raise a temperature ofall of the layer of feed material simultaneously to a temperaturesufficient to cause the first feed material to fuse.
 2. The system ofclaim 1, wherein the heat source comprises an array of heat lampsconfigured to heat all of the layer simultaneously.
 3. The system ofclaim 1, wherein the heat source comprises a plasma source.
 4. Anadditive manufacturing system comprising: a platen; a feed materialdispenser apparatus configured to deliver a first feed material over theplaten in a pattern specified in a computer-readable medium to form alayer of feed material over the platen; a heat source configured toapply heat simultaneously to a region of the layer of feed materialextending across a width of the platen and to scan the region across alength of the platen; and a controller configured to cause the heatsource to raise a temperature of the region of the layer of feedmaterial simultaneously to a temperature sufficient to cause the firstfeed material to fuse.
 5. The system of claim 4, wherein the region issubstantially linear and the heat source is configured to scan theregion in a direction perpendicular to a primary axis of the region. 6.The system of claim 5, wherein the heat source comprises a laser togenerate a laser beam and the system comprises optics that receive thelaser beam and expand a cross section of the laser beam along the widthof the platen.
 7. The system of claim 4, wherein the heat sourcecomprises a linear array of heat lamps.
 8. The system of claim 4,comprising an actuator coupled to at least one of the heat source orplaten to cause the region to scan across the length of the platen.9-15. (canceled)
 16. The system of claim 1 or 4, comprising a secondaryheat source configured to raise the layer of feed material to atemperature below a temperature at which the first feed material fuses.17-18. (canceled)
 19. The system of claim 16, wherein the controller isconfigured to cause the heat source to apply heat to all of the layer offeed material simultaneously after the secondary heat source heats thelayer of feed material.
 20. The system of claim 1 or 4 wherein the feedmaterial delivery system comprises a first dispenser configured todispense the first feed material and a second dispenser configured todispense a second feed material, the layer of feed material comprisingthe first material and the second material.
 21. The system of claim 20,wherein the first feed material fuses at a first temperature and thesecond feed material fuses at a second temperature, the firsttemperature being lower than the second temperature.
 22. The system ofclaim 21, wherein the controller is configured to cause the heat sourceto raise the temperature of the layer of feed material simultaneously toa temperature below the second temperature. 23-26. (canceled)
 27. Thesystem of claim 20, wherein the first dispenser and the second dispensereach comprises a gate that is individually controllable and the gate isconfigured to release respective first or second feed material atlocations on the platen according to the pattern specified in thecomputer-readable medium.
 28. The system of claim 27, wherein the gatecomprises an element selected from the group consisting of apiezoelectric printhead, a pneumatic valve, a microelectromechanicalsystems (MEMS) valve, a solenoid valve and a magnetic valve.
 29. Thesystem of claim 1 or 4, wherein the feed material delivery systemcomprises a line of dispensers configured to deliver a line of feedmaterial simultaneously, the line of dispensers configured to betranslated across the platen to deliver a layer of feed material. 30.The system of claim 1 or 4, wherein the feed material delivery systemcomprises a two dimensional array of dispensers configured to deliverall of the layer simultaneously.
 31. A method of additive manufacturing,comprising: dispensing a layer of a first feed material over a platen ina pattern specified in a computer-readable medium; and heating all ofthe layer of feed material simultaneously above a temperature at whichthe first feed material fuses.
 32. A method of additive manufacturing,comprising: dispensing a layer of feed material over a platen in apattern specified in a computer-readable medium; simultaneously heatinga region of the layer of feed material that extends across a width ofthe platen to a temperature above a temperature at which the feedmaterial fuses; and scanning the region across a length of the platen.33. (canceled)